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A Memoir on the Uric Acid. 393 
sequence of his having employed the mild, 
instead of the caustic alkalis. Nitric acid, 
however, he found to act on the stone with an 
effervescence, which he shews to be owing to 
the formation of a permanent gas.(d) 
No further examination appears to have 
been made of this substance for nearly half a 
century ; for it was not till the year 1776, that 
Scheele published the excellent essay, which 
contains the first accurate history of its che- 
mical properties.(e) With Hoffman and 
Hales, he found the matter of calculus * to 
be soluble in nitric acid ; and he added the 
observation, that by evaporating the solution 
to dryness, a red mass is obtained, which 
imparts its peculiar colour to the skin and 
other animal substances. This property is of 
importance, inasmuch as it distinguishes the 
body in question from all others. Scheele, 
also, first pointed out its title to be ranked. 
among acids, in consequence of its reddening 
the infusion of turnsole.. He determined, 
moreover, that the acid, which he had found 
(d) Hales’s Heemastatics 1727, p. 190. 
(e) Scheele’s Essays, Essay IX. 
* It is necessary to remark that this applies to one spe- 
cies of calculus only ; and that there are several kinds, dif- 
fering not only in external appearance but in chemical 
composition. 
3D 
